This invention relates to the formation of a copper electrode on aluminum nitride, especially on a sintered aluminum nitride body.
Aluminum nitride has an about five-fold greater thermal conductivity than alumina and sintered aluminum nitride bodies are well known to have the great advantages of excellent thermal conductivity and low coefficient of thermal expansion. It is expected that the sintered aluminum nitride bodies having such advantages can be metallized such that they are useful as various structural materials and electronic part-supporting materials including circuit boards requiring heat dissipation capacity, silicon chip protecting discs for power transistors and integrated circuits, and packages for power transistors and integrated circuits.
Unfortunately, it is generally difficult to bond metal with aluminum nitride. A number of bonding methods were proposed, for example, a thick film method wherein metal paste is applied and a method as disclosed in Japanese Patent Application Kokai No. 59-121175 wherein a sintered aluminum nitride body is surface treated before metallizing is carried out. The metallized bodies by these methods are often insufficient in bond strength between aluminum nitride and metal. In the method disclosed in Japanese Patent Application Kokai No. 59-121175, an oxide film is formed on a sintered aluminum nitride body during surface treatment to adversely affect the thermal conductivity thereof. These products were thus used in limited applications.